Architects and builders throughout the ages have chosen stone for its permanence and beauty. Where selection was once limited mainly to what was locally available, today’s stone marketplace is virtually worldwide. With the broad and growing array of options, the stone selection process has become more complex under the weight of multiple considerations.
STONE IS A NATURAL PRODUCT
Dimension stone has its own unique qualities that not only distinguish it from man-made materials, but also should be considered in selecting it for a particular project. Stone is not manufactured; it is a product of nature. Blocks are removed from the quarry, slabs are cut from these blocks, and the slabs are further fabricated into the final stone to be installed. Each block is different; each slab is different. Skillful blending or matching of the dimension stone blocks, veneer panels, tops, etc., results in a beautiful blending of nature’s variety and man’s design. In contrast to the uniformity of materials produced by machine or assembly line, dimension stone’s naturally varied appearance has wonderful character. “Uniformity of material,” when applied to natural stone, is a term of relative value that needs to be understood when making a selection.
Exterior vs. Interior Installations. The factors to be weighed in selection may not be equally applicable to exterior and interior installations. The following discussion is therefore divided, as appropriate, between exterior and interior uses if the factors do not readily apply to both.
Selection Influencers. While any number of stipulations may direct selection of a particular stone for a specific application, there are several significant influencing factors. Among them are aesthetics, color, strength, durability, design, texture, finish, size, thickness, availability, granite testing, stone sampling, and cost. The effects any of these factors may have on another can influence the final choice. But aesthetic considerations nearly always drive the selection process.
ASTHETICS & APPEARANCE
Factors Beyond Appearance. A palette of colors and a variety of textures provide ready options in the aesthetic choices among dimension stones. Yet, as the following pages suggest, it is advisable to examine and apply other factors that may recommend alternatives to a selection based purely upon aesthetic appeal, particularly on exterior applications. A stone that is most desirable in appearance, for example, may lack needed strength or durability for a particular application. Exterior Cautions. The cautions regarding exterior applications are of far less concern when considering interior installations. Aesthetics can be allowed much freer rein for stone that is not subjected to the elements.
Variegated or veined materials, especially marbles, that offer interesting colors and patterns and that are by their nature “faulted” and not generally suitable for exterior use are often highly valued for their decorative qualities in interior installations.
Translucence occurs in some white or very lightly colored marbles and onyxes having a crystal structure that will transmit light to varying degrees depending upon stone thickness and finish. Translucence can be an aesthetically intriguing decorative attribute.
Sample Variations. Assuming that all critical factors support the desired choice in a given application, expectations as to final appearance must be realistic. Unless a choice is made and marked on an actual slab, variation from a submitted sample is a fact and should not come as a surprise.
Fleuri Cut Stones. Many dimension stones today are being cross cut or fleuri cut. This is true in travertines and some granites, for example. Many times, the reason this is done is to avoid a directional vein and achieve a more “cloudlike” effect. In any case, the Specifier and the Stone Supplier should know if this is done and investigate the test data, as it may change from normal, conventional means. See illustration at the close of chapter
Filling Might Be Required. Another issue is where cross cut (fleuri cut) stones are used. As in the case of travertine, a limestone, it may require filling with cement or epoxy, which may or may not hold up under heavy traffic conditions, and the fills may come out.
Choosing A Finish. Choosing the manner in which stone will be finished is an integral part of the selection process. Finish can be anything from saw cut to high polish. A high polish will bring out the color of the stone to its fullest, because it will optimally reflect the light. Conversely, a textured finish will always appear lighter. A combination of finishes can add interest to a chosen stone. New finishes are appearing on the market yearly, so check and investigate all finishes available with your Stone Supplier.
Finishes commonly available are:
Acid Washed: Usually applied to a sawn finish to lower the degree of sawn marks showing, yet maintain a natural textured finish.
Bush-hammered: Coarsely textured surface produced by hammering, and may vary according to the metallic head used, from fine point to very coarse, and may leave high, lighter-colored markings.
Gauged: Done by a machine, usually with circular abrasives to grind the material to a specific thickness.
Honed: Dull sheen, without reflections, achieved by abrasive heads. The degree of honing depends on the stone, but may vary from light to heavy.
Fine Rubbed: Smooth and free from scratches; no sheen.
Flamed or Thermal: Plane surface with flame finish applied at high temperature by mechanically controlled means to ensure uniformity; changes the color of the stone.
Natural Cleft: A cleavage face formed when the stone is split into any thickness.
Picked, Hand-hewn Rock Face: Using a chisel or other metallic object that gives deeper indentations and cleavage to the stone.
Planed: Usually refers to slate, where a metallic scraper peels a layer of stone, making the stone flat and smoother.
Polished: Mirror gloss, with sharp reflections.
Sandblasted: Coarse plane surface produced by blasting an abrasive, allowing a fine-textured finish; may lighten the color.
Sawn: Usually refers to slabs coming from a gang saw, with blades that are applied to the block of stone using water and fine grit.
Tumbled: Method of putting tiles in a mixing container with sand and rotating them, allowing the edges and corners of} the tiles to chip.
Water-jet Flamed Finish: Gives a more uniform, textured finish and allows more of the natural color to show.
NOTE: Many new finishes are being applied to stone as the market demand increases and new uses for stone are being conceived. In some productions, combinations of finishes on the same stone are being made. Check with your granite supplier to verify the finish and how it was made in order to specify properly.